Astronomer and naturalist, b. at London, 9 Nov., 1789; d. at Brussels, 2 Feb., 1860. His literary education was neglected, as his father, a distinguished botanist, was a follower of Rousseau. He made up this deficiency, and during his lifetime became master of a number of modern languages. His early studies were, however, desultory, and he seems to have put off the choice of a profession until some years after attaining to man's estate. As early as 1805 he had compiled a "Journal of the Weather" and had published his "Liber Rerum Naturalium". A year later, inspired by Gall's works, he took up the study of phrenology. The comet of 1811 aroused his interest in astronomy, a science which he continued to pursue, and eight years later, on 3 July, 1819, he himself discovered a new comet. He finally matriculated at Corpus Christi College, Cambridge, in order to study law, but soon abandoned it to study medicine, taking his degree in 1819. Two years before, he had married the daughter of Colonel Beaufoy and taken up his residence at Spa Lodge, Tunbridge Wells. After the birth of his only daughter he moved to Hartwell in Sussex, and then went abroad, where he spent three years. His observations and studies on the Continent led to the publication, in 1824, of his "Perennial Calendar". It was also during this period that he was attracted by the claims of the Catholic Church, to which he became a convert. After his return to England he became a fellow of the Royal Astronomical Society and helped to found a meteorological society, which, however, had but a brief existence.

His father died in 1825, and he soon after took up his residence in Chelmsford in order to be near his daughter, who was a pupil at Newhall Convent. Here he undertook a series of researches on the influence of atmospheric conditions on diseases, and particularly on cholera. In 1830 he collected and published the letters of Locke, Shaftesbury, and Algernon Sydney. In 1833 he again went abroad, where he spent most of his remaining years, settling finally in Bruges. He continued his literary activity during the latter part of his life, some of his writings being poetical. He also composed selections for the violin. Forster was remarkable for his versatility and industry. He numbered among his friends many of the prominent authors and scholars of his time, such as Gray, Porson, Shelley, Peacock, Herschel, and Whewell. Besides the works mentioned, he also wrote, "Researches About Atmospheric Phenomena" (London, 1812; 2nd ed., 1823); "Reflections on the Destructive Operation of Spirituous Liquors" (London, 1812); "Pocket Encyclopedia of Natural Phenomena" (from his father's MSS., 1826); "Beobachtungen uber den Einfluss des Luftdruckes auf das Gehor" (Frankfort, 1835); "Observations sur l'influence des Cometes" (1836); "Pan, a Pastoral" (Brussels, 1840); "Essay on Abnormal Affections of the Organs of Sense" (Tunbridge Wells, 1841); "Annales d'un Physicien Voyageur" (Bruges, 1848); and numerous articles in "The Gentleman's Magazine".